Heat is generated at a secondary battery such as a lithium-ion battery as it is charged or discharged. An excessive rise in the battery temperature resulting from heat generation will adversely affect the battery performance. For instance, the battery output characteristics are likely to become degraded. In a device proposed in the related art in order to address this issue, the highest temperature inside a battery pack configured by combining a plurality of lithium-ion batteries is estimated and the input/output power at the battery pack is restricted based upon the estimation results (PTL 1).